Canary Cream

Have the appearance and taste of ordinary custard creams, but transfigure the eater into a huge canary. The effect is short-lived, however, since the person moults a few moments later and becomes his or her normal self.

Fred and George placed a hex on seemingly innocent custard creams so that whomever ate one was changed temporarily into a huge canary. Neville ate one of these Canary Creams, much to the amusement of everyone in the Gryffindor common room (GF21).